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Chapter 18: Q15 P (page 456)

Vapor at a pressure of 30.3μtbar from the solid compound pyrazine had a transmittance of 24.4% at a wavelength of 266nm in

a 3.00 - cm cell at 298K

Pyrazine

(a) Convert transmittance to absorbance.

(b) Convert pressure to concentration (mol/L) with the ideal gas law (Problem 1-18).

(c) Find the molar absorptivity of gaseous pyrazine at 266nm.

Short Answer

Expert verified
  1. Absorbance is 0.613.
  2. Pressure is1.67×10-5M-1cm-1..
  3. Molar absorptivity is 1.22×10-6..

Step by step solution

01

Absorbance.

Absorbance (A), also known as optical density (OD), is the quantity of light absorbed by a solution. Transmittance is the quantity of light that passes through a solution.

02

Calculation of Absorbance.

As

A = - log(T)

Therefore,

A = - log(0.244)

A = 0.613

03

Calculation of the concentration of gas related to pressure.

As

c=nV

Also,

c=pR⋅Tc=30.3⋅10-6bar0.08314L⋅bar/mol⋅K⋅298Kc=1.22⋅10-6M

04

The value of Molar absorbance.

As absorbance is

A=ε⋅c⋅b

Therefore,

ε=Ac⋅bε=0.6131.22⋅10-6M⋅3cmε=1.67⋅105M-1cm-1

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Total role="math" localid="1663647483742" μLPb2+added

Absorbance at 490nmwavelength

Total μLPb2+added

Absorbance at490nmwavelength

0.0

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12.0

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24.0

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